Carbon black pellets and a process for the production thereof

Abstract

Carbon black pellets which can be produced by the addition of wax during dry granulation of carbon black powder. The carbon black pellets are distinguished by a pellet hardness of at least 0.15 N with a wax content of less than 10 wt. %, based on the total weight of the carbon black pellets.

We claim: 
     
       1. Carbon black pellets, comprising: carbon black; and at least one natural or synthetic wax, the carbon black pellets having a wax content of from 1 to less than 10 wt. %, based on a total weight of the carbon black pellets, wherein individual carbon black pellets have a hardness of greater than 0.15 N, and wherein the carbon black pellets are produced by pelletizing a powdered starting carbon black. 
     
     
       2. The carbon black pellets according to claim 1, wherein the starting carbon black has a DBP adsorption of from 40 to 250 ml/100 g and a nitrogen surface of from 5 to 500 m 2  /g. 
     
     
       3. The carbon black pellets according to claim 2, wherein the wax is a member selected from the group consisting of one or more paraffin waxes. 
     
     
       4. A process for continuous production of carbon black pellets according to claim 1, comprising: feeding carbon black powder into an inlet region of a pelletizing machine having a shaft with pins, the pelletizing machine further having a granulation region and an outlet region; adding a molten wax or a molten wax mixture to the pelletizing machine by atomizing said wax or wax mixture in a first third of the granulation region over the carbon black, which is still in powder form, wherein the atomized molten wax or molten wax mixture has an average droplet size not exceeding 50 μm, wherein a maximum circumferential speed of tips of the pin is from 1 to 6 m/s, and wherein an average residence time of the carbon black in the pelletizing machine is from 20 to 600 seconds; and continuously removing pelletized carbon black at the outlet region of the pelletizing machine. 
     
     
       5. The process according to claim 4, wherein the wax mixture is atomized over the carbon black, through 2 to 5 nozzles, the nozzles being arranged in a plane perpendicular to an axis of the shaft. 
     
     
       6. The process according to claim 5, wherein up to 50 wt. % of pre-densified carbon black is mixed with the carbon black powder as granulation seeds. 
     
     
       7. The process according to claim 5, wherein 5 to 30 wt. % of pre-densified carbon black is mixed with the carbon black powder as granulation seeds. 
     
     
       8. The process according to claim 5, further comprising pre-densifying the carbon black powder to a pour density of from 150 to 300 g/l before granulation. 
     
     
       9. The process according to claim 4, wherein no liquid is added to the pelletizing machine other than the molten wax or molten wax mixture. 
     
     
       10. The process according to claim 4, further comprising heating said pelletizing machine to a temperature from 10 to 20% above a melting temperature of the wax or wax mixture. 
     
     
       11. The process according to claim 4, further comprising atomizing said wax or wax mixture with compressed air. 
     
     
       12. The process according to claim 4, further comprising atomizing said wax or wax mixture from a plurality of nozzles arranged in a plane perpendicular to said shaft to obtain homogeneous mixing of wax and carbon black.